This application claims the priority of German Application No. 10 2006 056 627.0, filed Nov. 30, 2006, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method and a device for ensuring the standstill of a motor vehicle using at least one electronic control unit, by which the motor vehicle is braked down to a standstill while maintaining a specific distance to a target object.
Vehicles which have a speed (velocity) regulator utilizing distance sensors are already on the market. Such a vehicle attempts to maintain a predefinable driving speed, in particular during travel on a freeway or an expressway, but reduces this speed when this vehicle approaches a leading vehicle (target object). Extremely comfortable driving in column traffic is thus made possible for the vehicle driver, because the speed regulator having distance sensors (e.g., a so-called ACC “Adaptive/Active Cruise Control”) always maintains a sufficient safety distance to the “man in front.” If the lead vehicle accelerates, the speed regulator having distance sensors (also referred to as “ACC system” in the following) thus also accelerates the vehicle equipped therewith, until reaching the set desired speed or the speed of the lead vehicle, if the lead vehicle travels more slower than the desired velocity.
Reference is made to German patent document DE 101 52 632 A1 on the technical background, for example.
As a supplement to ACC systems, which are predominantly operated in a high speed range on well-structured roads, so-called stop & go systems, which allow for comparable driver support, in particular in the low velocity range down to standstill of the vehicle, are also known. In addition to high-performance close range sensors, these systems require an electronically activatable braking system, which is capable of reliably holding the vehicle in a stoppage phase and preventing further rolling until the driver of the vehicle or the stop & go system itself has given a corresponding command to start (start command).
An important function of an ACC stop & go system is the automatic stopping and secure retention of the vehicle at a standstill. Above all, if the vehicle is located on an incline, it is very important that (undesired) rolling backward of the vehicle is prevented.
A distance-related speed regulation system having a stop & go function, which particularly ensures the stoppage of the vehicle even with a predominantly level roadway, is described, for example, in German patent application 10 2005 036 217 (no prior publication).
An improved distance-related speed regulation system of the above type having a stop and go function is needed, in particular, for maintaining a standstill when stopping on hills.
The present invention provides a method for ensuring the standstill of a motor vehicle using at least one electronic control unit, by which the motor vehicle is braked down to a standstill while maintaining a specific distance to a target object. Before reaching the standstill, it is checked by the control unit, whether a predefined inclination threshold (N>S1) is exceeded, whether the velocity has fallen below a predefined travel velocity threshold (v<S2), and whether a negative vehicle acceleration (a<0) exists. If these conditions exist simultaneously, an increased setpoint braking torque is predefined by the control unit until the standstill of the vehicle is reached. Advantageous refinements of the invention are described and claimed herein.
From a specific incline, the stopping is prepared if the following two conditions are additionally fulfilled: (a) the vehicle velocity falls below a (preferably incline-dependent) threshold, and (b) the vehicle acceleration is negative (deceleration).
The present invention is based on the following findings.
To prepare for stopping, the brake is activated in such a way that secure retention of the vehicle is achieved. The background is as follows: regulated stopping uphill would normally be achieved by activating the drive, as also according to German patent application 10 2005 036 217, for example. This means that the vehicle would come to a standstill having a braking torque of zero [Nm]. According to German patent application 10 2005 036 217, the brake would then be activated to build up an (incline-dependent) safety reserve, which is necessary to retain the vehicle at a standstill uphill. Because the brake control unit requires a certain time until pressure is built up and the braking torque requested by ACC stop & go is available, the vehicle may roll backward unintentionally shortly after stopping. The stopping on the hill is “predicted” and correspondingly prepared for by the present invention. The ACC stop & go requests a braking torque already shortly before the stopping and the brakes may react more rapidly to the increased demand at a stop.
The instantaneous inclination at which the vehicle is located is calculated, for example, from the difference between the current value of the signal, which the longitudinal acceleration sensor provides, and the current value of the vehicle longitudinal acceleration, which is produced from the wheel speed sensors. Because this signal oscillates strongly during the transition from travel to standstill, this signal is preferably filtered by a low-pass filter.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.